The present invention relates to a spacer for use between recorded discs which are arranged in a stack, and particularly to a spacer which prevents any dust, dirt or other contaminating particles from scratching or otherwise damaging the disc playing area.
Recorded discs generally comprise a circular, flat plate or disc of a plastic material having a center hole therethrough and recorded information provided thereon in the form of a surface relief pattern formed along a spiral path in the major surfaces of the disc. The surface relief patterns preferably are formed in a spiral groove in the surfaces of the disc. The center portion and an outer edge portion of the major surfaces is generally left blank. Recently, there has been developed a high density recorded disc, such as a video disc, in which there are a large number of grooves per inch of the diameter of the disc, e.g. 10,000 grooves per inch (4000 grooves per cm). Because of the large numbers of these grooves, they are very narrow and shallow, i.e. 27 microns in width and 4000 Angstroms in depth. Because of the fineness of these grooves, any scratches in the surface of the disc can severely disrupt the operation of the disc and their presence is therefore highly undesirable.
The recorded discs are generally made in a mold press which includes a mold in which the discs are formed and a mechanism for removing flash from around the outer edge of the molded disc. From the flash removing mechanism the disc is transferred to a rack which is a base plate having a cylindrical rod projecting upwardly therefrom. The discs are stacked on the rack with the rod extending through the center holes in the disc. In order to prevent distortion and warping of the discs as they cool, a thin metal spacer plate is periodically placed between the discs, such as every fifth to tenth disc, so as to provide a more uniform distribution of the weight of the disc on the discs below. However, if any dust, dirt or other type of contaminating particles fall on the disc just beneath the spacer plate or on the surface of the spacer plate in the playing area, the spacer will press the particles into the surfaces of the adjacent discs, causing dents, scratches and the like in the playing surfaces of the discs. In view of the very small size of the grooves in the disc, such dents and scratches can disrupt the information on a large number of the grooves which will adversely effect the playing of the disc.